Systems and methods for protecting a semiconductor device

ABSTRACT

Circuits and methods for protecting a device are provided. A first device to be protected includes a gate dielectric of a first thickness. A second device includes a gate dielectric of a second thickness that is less than the first thickness. A gate is shared by the first device and the second device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/226,995, entitled “Systems and Methods for Protecting aSemiconductor Device,” filed Aug. 3, 2016, which is incorporated hereinby reference in its entirety.

BACKGROUND

Integrated circuits and other semiconductor devices are formed toinclude a multitude of individual transistors coupled together and tovarious other features to form functional devices. If any one of thetransistors fails, device functionality can be destroyed. In advancedsemiconductor device fabrication and manufacturing, plasma chemistryoperations are used multiple times in the sequence of fabricationoperations used to form integrated circuit and other semiconductordevices. Plasma operations include plasma etching operations and plasmadeposition operations. Plasma vapor deposition, PVD, and plasma enhancedchemical vapor deposition, PECVD, represent just two of many plasmadeposition operations.

The plasma operations utilize excited ions, and these ions are directedto a surface of a substrate on which a device is formed, often at highbiases. The highly sensitive transistors utilized in integrated circuitsand other semiconductor devices commonly include gates (e.g., gatesincluding polysilicon or metal) positioned over a gate dielectric whichmay be an oxide or other gate dielectric material. During plasmaoperation, charge accumulates on the gates, and the accumulated chargeresults in an increased voltage across the gate dielectric. If thevoltage across the gate dielectric exceeds a threshold (e.g. , 10MV/cm), charge passage through the dielectric can cause damage thatcreate traps in an interface between the dielectric and an underlyingsubstrate (e.g., a silicon substrate). Plasma induced gate dielectricdamage is commonly referred to as the antenna effect and is an effectthat damages transistor gates and the transistor gate dielectricmaterials. Such damage can potentially cause yield, reliability, andnoise problems during the manufacture of MOS integrated circuits. Devicefunctionality can be destroyed if the gate dielectric damage is severe.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 depicts an example circuit for protecting a critical device, inaccordance with some embodiments.

FIG. 2A depicts an example layout of a circuit for protecting a criticaldevice, in accordance with some embodiments.

FIG. 2B depicts an example equivalent circuit for the circuit of FIG.2A, in accordance with some embodiments.

FIG. 3A depicts an example layout of another circuit for protecting acritical device, in accordance with some embodiments.

FIG. 3B depicts an example equivalent circuit for the circuit of FIG.3A, in accordance with some embodiments.

FIGS. 4A and 4B depict use of dummy devices having sharp angles forprotecting a critical device, in accordance with some embodiments.

FIG. 5 depicts operations of an example method for protecting a criticaldevice, in accordance with some embodiments.

FIG. 6 depicts operations of another example method for protecting acritical device, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The manufacture of large scale integrated circuits in a mass productionfacility involves hundreds of discrete processing steps beginning withthe introduction of blank semiconductor wafers at one end and recoveringthe completed chips at the other. The manufacturing process includes asegment where semiconductor devices are formed within a semiconductorwafer and a segment which includes the formation of the various layersof interconnection metallurgy above a surface of the semiconductorwafer. Most of these processing steps involve depositing layers ofmaterial, patterning them by photolithographic techniques, and etchingaway the unwanted portions. The materials primarily include insulatorsand metal alloys. In some instances the patterned layers serve astemporary protective masks. In others they are the functional componentsof the integrated circuit chip.

Radio-frequency (RF) plasmas may be used extensively in many of theseprocessing steps. Reactive-ion-etching (RIE) provides the etchinganisotropy required to achieve a high degree of pattern definition andprecise dimensional control. Here the gaseous chemical etching isassisted by unidirectional ion bombardment provided by an RF plasma.Photoresist layers, too, are frequently removed, not by chemicalsolvents, but more cleanly by plasma ashing.

A metal-oxide-silicon-field-effect-transistor (MOSFET) is a deviceconsisting of two shallow regions of one type semiconductor—the sourceand the drain—separated by a region of another type. The conductivity ofthe central region (channel) is modulated by applying a voltage to anelectrode (gate) which overlies the channel region and is separated fromit by a thin insulating layer (i.e., gate dielectric comprising anoxide). CMOS (complementary MOS) technology utilizes MOSFETs in pairs,one an n-type channel device (NMOS) and the other a p-type channeldevice (PMOS). The simple nature of these devices and their minimal heatdissipation permits an extraordinary degree of miniaturization andconsequently a high density of circuits.

The gate dielectric which overlies the channel region includes athermally grown silicon oxide, in some embodiments. The insulating filmis highly susceptible to damage from external sources (e.g., highelectric fields, etc.) during manufacture. A prominent cause of suchdamage is ion and electron bombardment from plasmas used while formingthe various layers. The surfaces of patterned semiconductor waferslocated within a plasma reactor present multiple areas of conductors andinsulators to the plasma. These produce local non-uniformities in theplasma currents which result in charge build-up on the electricallyfloating conductor surfaces.

After the gate dielectric is formed, it is covered with a layer ofconductive material (e.g., polysilicon, metal, etc.) within which thegate electrode is defined. The etching of this conductive layer may beaccomplished by reactive-ion-etching, providing the first in a series ofexposures of the gate dielectric to an RF plasma. In this instance, thearea of the gate electrode is covered with photoresist. As etchingproceeds, the exposed conductive material provides sufficient conductionto prevent local charge build-up. However, as the endpoint isapproached, the conductive layer breaks up and residual, now isolated,regions of conductive material surrounding the photoresist protectedgate electrode act as an antenna which accumulate positive charge. Thisresults in the development of a positive potential sufficiently high tocause current flow through the gate dielectric. These conductivematerial halos can present a high antenna-to-thin dielectric area ratiocausing massive current flow in the gate dielectric. As etchingproceeds, the halos of conductive material disappear and the antennaarea is reduced to the thin edges of the gate electrode itself.

The mechanism of current flow though the gate dielectric is primarilyFowler-Nordheim (FN) tunneling. FN tunneling occurs at fields in excessof 10 MV/cm. Charge build up on the gate electrode resulting in a gateelectrode potential of only 10 volts is therefore sufficient to induceFN tunneling through a dielectric layer of 100 Angstroms. Suchpotentials are easily achieved in conventional plasma reactors.Excessive FN tunneling currents eventually lead to interface traps inthe gate dielectric. Such trap sites can cause random telegraph signal(RTS) noise and/or flicker noise in devices, both of which areundesirable.

A consequence of these numerous exposures of semiconductor wafers to RFplasmas and other forms of ionic radiation is the potential occurrenceof radiation damage and the accumulation of charge on exposed conductivecomponents which leads to damaging current flows and trapped chargeaffecting the semiconductor devices. Thus, plasma induced damage is awell-known issue during the semiconductor wafer manufacturing process.Sometimes referred to as the “antenna effect” or “plasma induced gatedielectric damage,” plasma induced damage refers to the chargeaccumulation in isolated nodes during the processing of an integratedcircuit. Such damage may affect the reliability and performance of theintegrated circuit device. Plasma induced damage can occur at variouspoints in the processing flow. For example, plasma induced damage canoccur during etching of a gate (e.g., a gate comprising polysilicon ormetal, as described above), during etching of material (e.g., metal) toform contacts and vias, and during plasma ashing processes used toremove photoresist.

The approaches of the instant disclosure provide systems and methods forprotecting an integrated circuit device from plasma induced gatedielectric damage (e.g., that occurs during the processing of thedevice). In embodiments described herein, both a “critical device” and a“dummy device” are fabricated. As referred to herein, a “criticaldevice” is a device (e.g., a MOSFET-based, integrated circuit device)that is to be protected from damage (e.g., plasma induced gatedielectric damage that occurs during processing of the critical device).As referred to herein, a “dummy device” is a device that is used for thepurpose of protecting the critical device from damage. The criticaldevice and the dummy device share a common gate (e.g., a gate comprisingpolysilicon or metal, etc.). During the processing of the devices, whencharge accumulates on the gate, the dummy device presents a lowerbarrier to the discharging of the accumulated charges, in comparison tothe critical device. Consequently, carrier tunneling (e.g., FNtunneling) occurs in the dummy device, but does not occur in thecritical device. The non-critical dummy device thus experiences plasmainduced gate dielectric damage but the critical device is protected fromany such damage. The approaches of the instant disclosure areimplemented in several embodiments described below.

FIG. 1 depicts an example circuit for protecting a critical device 102,in accordance with some embodiments. The example circuit includes thecritical device 102 and a dummy device 106, which are formed on a commonsubstrate 120. Shallow trench isolation (STI) insulator material 110 isdisposed between the critical device 102 and the dummy device 106 andelectrically isolates portions of the devices 102, 106 from one another.In the embodiment of FIG. 1, the critical device 102 has a gatedielectric 104 of a first thickness, and the dummy device 106 has a gatedielectric 109 of a second thickness that is less the first thickness.The respective gate dielectrics 104, 109 comprise oxide materials (e.g.,silicon dioxide, silicon oxide, etc.), in some embodiments. In anexample, the gate dielectric 104 of the critical device 102 has athickness within an approximate range of 30-100 angstroms, and the gatedielectric 109 of the dummy device 106 has a thickness within anapproximate range of 5-60 angstroms. It is noted that these thicknessesare only examples, and that in other embodiments, the gate dielectrics104, 109 have other thicknesses.

The critical device 102 and the dummy device 106 share a common gate108. The gate 108 comprises a conductive material, and in embodiments,the gate 108 comprises polysilicon or metal. As shown in FIG. 1, thegate 108 is formed over the gate dielectrics 104, 109 of the respectivecritical device 102 and dummy device 106. The gate 108 is also formed onthe STI insulator material 110 that separates the critical device 102from the dummy device 106. During processing (e.g., processing thatutilizes an RF plasma or another form of ionic radiation, such as RIEetching, etc.) of the critical device 102, charge accumulates on thegate 108, thus resulting in a voltage on the gate 108. With the gate 108being shared by the critical device 102 and the dummy device 106, avoltage drop over the critical device 102 is the same as that over thedummy device 106. In the embodiment of FIG. 1, a voltage drop betweenthe gate 108 and the substrate 120 is the same for both the criticaldevice 102 and the dummy device 106.

Although there is a same voltage drop over the critical device 102 andthe dummy device 106, an electric field present in the gate dielectric109 of the dummy device 106 is greater than an electric field present inthe gate dielectric 104 of the critical device 102. The higher electricfield in the gate dielectric 109 is a consequence of the gate dielectric109 being thinner than the gate dielectric 104. During the processing ofthe devices 102, 106, when charge 112 accumulates on the gate 108,carrier tunneling 116 (e.g., FN tunneling, etc.) occurs in the dummydevice 106 as a result of the higher electric field in the gatedielectric 109. Conversely, carrier tunneling does not occur in thecritical device 102, due to the lower electric field in the gatedielectric 104.

The dummy device 106 thus presents a lower barrier to the discharging ofthe accumulated charges 112, in comparison to the critical device 102.The dummy device 106 experiences plasma induced gate dielectric damagebut the critical device 102 is protected from any such damage.Consequently, the critical device is free of the above-described RTS.

The approaches of the instant disclosure differ from conventionalapproaches. One conventional approach is termed “design rule check”(DRC). Under the conventional DRC approach, various steps are taken tolower plasma induced gate dielectric damage (e.g., changes to metalrouting, adding embedded protection diodes, etc.). However, as describedabove, plasma induced damage commonly occurs during gate etching (e.g.,etching polysilicon, metal, etc.) and contact etching (e.g., before a M1metal layer process), and the DRC approach cannot reduce or eliminateplasma induced damage that occurs during these processes. Anotherconventional approach is termed “process improvement.” Under theconventional process improvement approach, a process recipe may bechanged to reduce plasma induced damage, and processes may be added torepair defects in the gate dielectric. However, this approach can onlyreduce plasma induced damage, and it cannot eliminate all plasma induceddamage. Another conventional approach relies on modifying anarchitecture of the device that is to be protected from plasma induceddamage. For example, in some approaches, one or more dimensions of thedevice to be protected are enlarged in order to reduce plasma induceddamage in the device. In these approaches, plasma induced damage isreduced or eliminated at the cost of a larger device size. Theseconventional approaches and others have various other deficiencies(e.g., process-based approaches may present bottlenecks in theprocessing flow, device-based approaches may have relatively highleakage current, etc.).

In contrast to these conventional approaches, the approaches of theinstant disclosure utilize a “circuit-based” solution that utilizes botha critical device and a dummy device, as described above. In contrast toone or more of the conventional approaches described above, thecircuit-based solution eliminates plasma induced damage that occursduring gate etching (e.g., etching conductive material for forming agate) and contact etching (e.g., before a M1 metal layer process).Further, the circuit-based solution may allow for all plasma induceddamage to be eliminated, in contrast to one or more of the conventionalapproaches that only minimize the damage without totally eliminating it.Additionally, in contrast to one or more of the conventional approachesdescribed above, the circuit-based solution of the instant disclosuredoes not require modification of the architecture of the critical deviceto be protected. Rather, the extra dummy device is added to protect thecritical device, and the architecture of the critical device isunchanged. The circuit-based approach of the instant application is sotermed because it relies on the formation of a “circuit” including thecritical device and the dummy device.

FIG. 2A depicts an example layout of a circuit for protecting thecritical device 102, in accordance with some embodiments. The layout ofFIG. 2A includes the critical device 102 formed in a first portion ofsemiconductor material 204 (e.g., a first semiconductor region 204) andthe dummy device 106 formed in a second portion of semiconductormaterial 202 (e.g., a second semiconductor region 202). In embodiments,each of the semiconductor regions 202, 204 comprises an active deviceregion (e.g., a transistor device area comprising source, drain, andchannel regions of a transistor device, etc.) including one or moresemiconductor structures (e.g., transistor structures, etc.) formedtherein. The semiconductor regions 202, 204 may be referred to as oxidedefinition (OD) regions. The semiconductor regions 202, 204 arespatially separated by the STI insulator material 110 that is disposedbetween the semiconductor regions 202, 204, and the STI insulatormaterial 110 provides electrical isolation between the semiconductorstructures formed in the respective semiconductor regions 202, 204. Inembodiments, the STI insulator material 110 surrounds all sides of thesemiconductor regions 202, 204, as depicted in FIG. 2A.

The single gate 108 is shared by the critical device 102 and the dummydevice 106, and during processing (e.g., processing that utilizes an RFplasma or another form of ionic radiation, such as RIE etching, etc.) ofthe devices 102, 106, charge accumulates on the gate 108, thus resultingin a voltage on the gate 108. With the gate 108 being shared by thecritical device 102 and the dummy device 106, a voltage drop over thecritical device 102 is the same as that over the dummy device 106. Thecritical device 102 has the thicker gate dielectric 104, and the dummydevice 106 has the thinner gate dielectric 109. Such gate dielectrics104, 109 are not visible in FIG. 2A but are depicted in FIG. 1,described above. As a result of the difference of the gate dielectricthicknesses, when charges accumulate on the gate 108 during processing,carrier tunneling occurs in the dummy device 106 before the criticaldevice 102. Accordingly, any plasma induced damage occurs in the dummydevice 106, and the critical device 102 is protected from such damage.

FIG. 2B depicts an example equivalent circuit for the circuit of FIG.2A, in accordance with some embodiments. As shown in the equivalentcircuit, the gates of the critical device 102 and the dummy device 106are tied together (e.g., via the common gate 108, described above). Inexamples, the critical device 102 is a column bias device (e.g., in aCMOS image sensor) that receives a column bias 208, as shown in FIG. 2B.Such column bias devices are examples of devices that are sensitive toRTS and that should be protected from plasma induced damage in order tominimize or eliminate RTS. Using the systems and methods of the instantapplication, such critical devices are protected from plasma induceddamage via the use of the dummy devices.

FIG. 3A depicts an example layout of another circuit for protecting acritical device 102, in accordance with some embodiments. The layout ofFIG. 3A includes the critical device 102 formed in a first portion ofsemiconductor material 304 (e.g., a first semiconductor region 304) andthe dummy device 106 formed in a second portion of semiconductormaterial 302 (e.g., a second semiconductor region 302). In embodiments,each of the semiconductor regions 302, 304 comprises an active deviceregion including one or more semiconductor structures (e.g., transistorstructures, etc.) formed therein. The STI insulator material 110surrounds the semiconductor regions 302, 304 and provides electricalisolation between the semiconductor structures formed in the respectivesemiconductor regions 302, 304.

In some circumstances, it may be desirable to minimize an area consumedby the dummy device 106. Thus, the example of FIG. 3A illustrates thatthe dummy device 106 can be made relatively small, as illustrated by therelatively small semiconductor region 302. As can be seen in the figure,the semiconductor region 302 of the dummy device 106 has an area that issmaller than that of the semiconductor region 304 of the critical device102. To minimize the size of the dummy device 106, the dummy device 106need not include a full transistor structure (e.g., full source anddrain regions, as are used in a full transistor structure), in examples.Further, to minimize the size of the dummy device 106, the dummy device106 need not connect to anything (i.e., with the exception of the dummydevice's connection to the critical device 102 via conductive layer106), in examples. Because the purpose of the dummy device 106 is onlyto protect the critical device 102 from plasma induced damage, therequirements of the dummy device 106 are minimal, and the dummy device106 can be made relatively small.

As in the example of FIG. 2A, the single gate 108 is shared by thecritical device 102 and the dummy device 106, and during processing ofthe devices 102, 106, a voltage is formed on the gate 108. Because thegate 108 is shared by the critical device 102 and the dummy device 106,a voltage drop over the critical device 102 is the same as that over thedummy device 106. The critical device 102 has the thicker gatedielectric 104, and the dummy device 106 has the thinner gate dielectric109. Such gate dielectrics 104, 109 are not visible in FIG. 3A but aredepicted in FIG. 1, described above. As a result of the difference ofthe gate dielectric thicknesses, a higher electric field is present inthe thinner gate dielectric 109, as compared to that of the thicker gatedielectric 104. When charges accumulate on the gate 108 duringprocessing, carrier tunneling occurs in the dummy device 106 before thecritical device 102, due to the higher electric field in the thinnergate dielectric 109. Accordingly, any plasma induced damage occurs inthe dummy device 106, and the critical device 102 is protected from suchdamage.

FIG. 3B depicts an example equivalent circuit for the circuit of FIG.3A, in accordance with some embodiments. As shown in the equivalentcircuit, the gate of each critical device 102 is connected to a gate ofa dummy device 106 (e.g., via a common gate 108, described above).During processing, charge builds up on a common gate shared by thedevices 102A, 106A, such that a same voltage 306 is present at gates ofboth of the devices 102A, 106A. Likewise, during processing, chargebuilds up on a common gate shared by the devices 102B, 106B, such that asame voltage 307 is present at gates of both of the devices 102B, 106B.

The equivalent circuit of FIG. 3B further includes a transistor 309 tiedto terminals (e.g., source terminals, drain terminals, etc.) of thedevices 102A, 102B. In examples, a bias voltage is received at a gateterminal of the transistor 309. In some embodiments, the equivalentcircuit of FIG. 3B is a portion of an operational amplifier orcomparator, and the transistor 309 is a bias device of the operationalamplifier or comparator. In examples, the equivalent circuit of FIG. 3Bincludes a differential input pair, with a first input being the biasvoltage 306, and a second input being the bias voltage 307. It is thusnoted that the use of one or more relatively small dummy devices (e.g.,as are utilized in the example of FIGS. 3A and 3B) may be suitable fordifferential input pair configurations and other configurations where adevice area must be kept relatively small. Further, in someapplications, a circuit design or device design is sensitive to loadingon the differential input pair, and the use of a dummy device asdescribed herein can increase a loading on the critical device 102(e.g., a loading on a gate of the critical device 102). Thus, use of oneor more relatively small dummy devices may reduce the loading on thecritical device 102, as compared to the loading that would be placed onthe critical device 102 by one or more larger dummy devices.

FIGS. 1-3B illustrate embodiments of the instant disclosure utilizing adummy device with a gate dielectric that is thinner than that of acritical device. In other embodiments, a different technique is used toprotect the critical device. For example, as described below withreference to FIGS. 4A and 4B, in embodiments, the dummy device has ashape that is configured to induce a local electric field concentrationin the dummy device during processing (e.g., processing that utilizes anRF plasma or another form of ionic radiation, such as RIE etching,etc.). Consequently, during the processing, an electric field in thedummy device is higher than an electric field in the critical device.When charge accumulates on the gate during the processing, carriertunneling occurs in the dummy device as a result of its higher electricfield. Conversely, carrier tunneling does not occur in the criticaldevice, due to its lower electric field.

To illustrate such embodiments, reference is made to FIGS. 4A and 4B,which depict use of dummy devices having sharp angles for protecting acritical device, in accordance with some embodiments. The layout of FIG.4A includes the critical device 402 formed in a first portion ofsemiconductor material 408 (e.g., a first semiconductor region 408) andthe dummy device 406 formed in a second portion of semiconductormaterial 410 (e.g., a second semiconductor region 410). In embodiments,each of the semiconductor regions 408, 410 comprises an active deviceregion. The semiconductor regions 408, 410 are spatially separated bythe STI insulator material 110 that is disposed between thesemiconductor regions 408, 410, and the STI insulator material 110provides electrical isolation between the semiconductor structuresformed in the respective semiconductor regions 408, 410. In someembodiments, the STI insulator material 110 surrounds all sides of thesemiconductor regions 408, 410, as depicted in FIG. 4A.

The single gate 108 is shared by the critical device 402 and the dummydevice 406. In particular, the gate 108 is formed over (i) gatedielectrics of the respective critical and dummy devices 402, 406, and(ii) the STI insulator material 110 (e.g., similar to what is depictedin FIG. 1). The semiconductor region 410 of the dummy device 406 hassharp angles 412 that cause a large, localized electric field in thedummy device 406 under the conductive layer 108 during the processing.The sharp angles 412 each include a point at which two lines meet. Theshape of the semiconductor region 410 thus comprises an hourglass shapewith (i) top and bottom rectangles having a first width “w1,” and (ii) amiddle portion between the top and bottom rectangles that tapers to asecond width “w2” that is less than the first width w1. It is noted thatthe shapes of the semiconductor regions 410, 460 of FIGS. 4A and 4B areonly examples, and that in other embodiments, different shapes usingrelatively sharp angles and/or corners are used.

With the large, localized electric field in the dummy device 406 causedby the sharp angles 412, an electric field in the dummy device 406 ishigher than an electric field in the critical device 402 during theprocessing. When charge accumulates on the gate 108 during processing ofthe devices 402, 406, carrier tunneling occurs in the dummy device 406as a result of its higher electric field. Conversely, carrier tunnelingdoes not occur in the critical device 402, due to its lower electricfield. Accordingly, any plasma induced damage occurs in the dummy device406, and the critical device 402 is protected from such damage. When theshape of the dummy device's semiconductor region is designed to induce alarge, local electric field during processing (as in the examples ofFIGS. 4A and 4B), the critical device and the dummy device may have asame gate dielectric thickness or may have different gate dielectricthicknesses.

The layout of FIG. 4B includes the critical device 452 formed in a firstportion of semiconductor material 458 (e.g., a first semiconductorregion 458) and the dummy device 456 formed in a second portion ofsemiconductor material 460 (e.g., a second semiconductor region 460).The semiconductor regions 458, 460 are spatially separated by the STIinsulator material 110. The single gate 108 is shared by the criticaldevice 452 and the dummy device 456. In particular, the gate 108 isformed over (i) gate dielectrics of the respective critical and dummydevices 452, 456, and (ii) the STI insulator material 110. Thesemiconductor region 460 of the dummy device 456 has sharp angles 462that cause a large, localized electric field in the dummy device 456under the conductive layer 108 during the processing of the devices. Theshape of the semiconductor region 460 comprises a rectangle with twotriangles protruding from sides of the rectangle. It is noted that thisshape is only an example, and that in other embodiments, differentshapes using relatively sharp angles and/or corners are used.

With the large, localized electric field in the dummy device 456 causedby the sharp angles 462, an electric field in the dummy device 456 ishigher than an electric field in the critical device 452 during theprocessing. When charge accumulates on the gate 108 during processing ofthe devices 452, 456, carrier tunneling occurs in the dummy device 456as a result of its higher electric field. Conversely, carrier tunnelingdoes not occur in the critical device 452, due to its lower electricfield. Accordingly, any plasma induced damage occurs in the dummy device456, and the critical device 452 is protected from such damage.

Although the examples of FIGS. 4A and 4B depict the critical device andthe dummy device as having similar sizes (e.g., similar areas), it isnoted that in other examples, the dummy device (e.g., dummy device 406,dummy device 456) can be fabricated to have a relatively small size. Theformation of dummy devices having relatively small sizes is describedabove with reference to FIGS. 3A and 3B.

FIG. 5 depicts operations of an example method for protecting a device.FIG. 5 is described with reference to FIG. 1 above for ease ofunderstanding. But the process of FIG. 5 is applicable to otherstructures as well. At 502, a first device (e.g., critical device 102)to be protected is formed, the first device including a gate dielectric(e.g., gate dielectric 104) of a first thickness. At 504, a seconddevice (e.g., dummy device 106) is formed, the second device including agate dielectric (e.g., gate dielectric 109) of a second thickness thatis less than the first thickness. At 506, a gate (e.g., gate 108) thatis shared by the first device and the second device is formed.

FIG. 6 depicts operations of another example method for protecting adevice. FIG. 6 is described with reference to FIG. 4A above for ease ofunderstanding. But the process of FIG. 6 is applicable to otherstructures as well. At 602, a first device (e.g., critical device 402)to be protected is formed. At 604, a second device (e.g., dummy device406) is formed, the second device having a shape that is configured toinduce a local electric field concentration in the second device. At606, a gate (e.g., gate 108) that is shared by the first device and thesecond device is formed.

The present disclosure is directed to circuits and methods forprotecting a device. An example circuit for protecting a devicecomprises a first device to be protected, the first device including agate dielectric of a first thickness. The circuit also includes a seconddevice including a gate dielectric of a second thickness that is lessthan the first thickness. The circuit further includes a gate that isshared by the first device and the second device.

Another example circuit for protecting a device includes a first deviceto be protected. The circuit also includes a second device having ashape that is configured to induce a local electric field concentrationin the second device. The circuit further includes a gate that is sharedby the first device and the second device.

In an example method for protecting a device, a first device to beprotected is formed, the first device including a gate dielectric of afirst thickness. A second device is formed, the second device includinga gate dielectric of a second thickness that is less than the firstthickness. A gate that is shared by the first device and the seconddevice is formed.

In another example method for protecting a device, a first device to beprotected is formed. A second device is formed, the second device havinga shape that is configured to induce a local electric fieldconcentration in the second device. A gate that is shared by the firstdevice and the second device is formed.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A circuit for protecting a device, the circuitcomprising: a first device to be protected; a second device having ashape that is configured to induce a local electric field concentrationin the second device; and a gate that is shared by the first device andthe second device.
 2. The circuit of claim 1, wherein the shapecomprises: a rectangle, and a triangle protruding from a side of therectangle.
 3. The circuit of claim 1, wherein the shape comprises anhourglass shape with (i) top and bottom rectangles having a first width,and (ii) a middle portion between the top and bottom rectangles thattapers to a second width that is less than the first width.
 4. Thecircuit of claim 1, wherein the first device and the second device areformed on a common substrate, the circuit further comprising: aninsulator material disposed between the first device and the seconddevice.
 5. The circuit of claim 4, wherein the gate is disposed on (i)gate dielectrics of the respective first and second devices, and (ii)the insulator material.
 6. The circuit of claim 1, wherein the seconddevice has an area that is less than that of the first device.
 7. Thecircuit of claim 1, wherein the second device is configured to inducethe local electric field concentration during processing of the firstdevice.
 8. A method for protecting a device, the method comprising:forming a first device to be protected; forming a second device having ashape that is configured to induce a local electric field concentrationin the second device; and forming a gate that is shared by the firstdevice and the second device.
 9. The method of claim 8, wherein theshape comprises: a rectangle, and a triangle protruding from a side ofthe rectangle.
 10. The method of claim 8, wherein the shape comprises anhourglass shape with (i) top and bottom rectangles having a first width,and (ii) a middle portion between the top and bottom rectangles thattapers to a second width that is less than the first width.
 11. Themethod of claim 8, wherein the first device and the second device areformed on a common substrate, the method further comprising: forming aninsulator material disposed between the first device and the seconddevice.
 12. The method of claim 11, wherein the gate is formed on (i)gate dielectrics of the respective first and second devices, and (ii)the insulator material.
 13. The method of claim 8, wherein the seconddevice has an area that is less than that of the first device.
 14. Acircuit for protecting a semiconductor structure, the circuitcomprising: a first semiconductor structure to be protected; a secondsemiconductor structure having a shape that is configured to induce alocal electric field concentration in the second semiconductorstructure; and a gate that is shared by the first semiconductorstructure and the second semiconductor structure.
 15. The circuit ofclaim 14, wherein the shape comprises: a rectangle, and a triangleprotruding from a side of the rectangle.
 16. The circuit of claim 14,wherein the shape comprises an hourglass shape with (i) top and bottomrectangles having a first width, and (ii) a middle portion between thetop and bottom rectangles that tapers to a second width that is lessthan the first width.
 17. The circuit of claim 14, wherein the firstsemiconductor structure and the second semiconductor structure areformed on a common substrate, the circuit further comprising: aninsulator material disposed between the first semiconductor structureand the second semiconductor structure.
 18. The circuit of claim 17,wherein the gate is disposed on (i) gate dielectrics of the respectivefirst and second semiconductor structures, and (ii) the insulatormaterial.
 19. The circuit of claim 14, wherein the second semiconductorstructure has an area that is less than that of the first semiconductorstructure.
 20. The circuit of claim 14, wherein the second semiconductorstructure is configured to induce the local electric field concentrationduring processing of the first semiconductor structure.